Dienes cyclohexa

An electron-withdrawing substituent leads to a product where it is bound to a saturated carbon center. Benzoic acid 9 is reduced to the cyclohexa-2,5-diene carboxylic acid 10 ... 

Generally, oxepins have a tendency to contract to a six-membered carbocycle when treated with acid. The driving force is the aromaticity of the phenol formed. However, when the less stable cyclohexa-2,5-diene-1,4-diol with an appropriate substitution pattern is treated with acid, the oxepin system is obtained. The treatment of cyclohexadienediols that are substituted with tert-butyl groups in the 2- and 6-positions and aryl at Cl and C4 with trifluoroacetic acid produces oxepins 1 with elimination of water.186 187 This reaction, however, is restricted to certain aryl substituents with at least some electron-donating effect. Generally, cyclohexa-2,4-dienone derivatives 2 are formed.187,188... 

Hexane (150 mL) was poured onto 2,6-di-/< rr-butyl-4-[(4-dimethylamino)phenyI]-T(4-tolyl)cyclohexa-2,5-diene-l,4-diol (5.0 g, 11.5 mmol) and heated under reflux. Then, EtOH was added in portions until all of the substance had been dissolved. Each addition of EtOH gave rise to a dark-red color of the mixture. The volume of the solution was reduced to allow the product to crystallize. The product was recrystallized (hexane) at low temperature yield 2.5 g (52%) mp 109°C. 

Bis-allylic oxidation of 23 and related cyclohexa-1,4-dienes provides a convenient and general preparation of cyclohexa-2,5-dien-l-ones (Scheme 7). These cross-conjugated die-nones are substrates for a variety of photochemical rearrangement and intramolecular cycloaddition reactions. Amide-directed hydrogenations of dienones 24a and 24b with the homogeneous iridium catalyst afford cyclohexanones 25a and 25b, containing three stereogenic centers on the six-... 

Reaction with p-benzoquinones.6 Fischer and Henderson have found conditions that result in 1,2-addition of various RLi reagents to p-benzoquinonc. The reaction when conducted in ether at —78° results in 4-alkyl-4-hydroxycyclohexa-2,5-diene-l-ones. These products undergo further 1,2-addition with RLi in THF to give dialkyl-cyclohexa-2,5-diene-l,4-diols. Mixed dienediols can be obtained by use of two different RLi reagents. 

Hydrosilation of an alkenylsilane in the presence of a catalyst provides a route to five-, six- and seven-membered rings but is of little use for the smaller ones. Tin-substituted cyclohexa-2,5-dienes result directly from the a,[Pg.575]

The 1,2-shift of pcrfluoroalkyl groups from carbon to carbon has been reported in an acyloin-like rearrangement of 4-hydroxy-4-(perfluorooctyl)cyclohexa-2,5-dien-l-one (19) to hy-droquinone 20.13... 

Keywords 4-(3-butenyl)cyclohexa-2,5-dien-l-one, inclusion complex, photocy-clization... 

Intramolecular hydroamination of cyclohexa-2,5-dienes has afforded the corresponding bicyclic allylic amines with high selectivity (Scheme 13).80 The reaction does not proceed through a direct hydroamination of one of the diastereotopic alkenes but more likely involves a diastereoselective protonation of a pentadienyl anion, followed by addition of a lithium amide across the double bond of the resulting 1,3-diene and a highly regioselective protonation of the final allylic anion. 

Intramolecular hydroamination of cyclohexa-2,5-dienes (204) mediated by Bu"Li has been reported to produce the corresponding bicyclic allylic amines (205) with high... 

Photoirradiation of inclusion crystals of the 4-(3-butenyl)cyclohexa-2,5-dien-l-ones (83) with the optically active host compounds (12c) in the solid state gave optically active l-carbomethoxytricyclo[4.3.1.0]dec-2-en-4-ones (84). For... 

The desymmetrization of 4-substituted-4-(3-formylpropyl)cyclohexa-2,5-dien-l-one 65 formed - in a single step - three contiguous stereocenters, including a quaternary stereocenter (Scheme 2.56). 

Carboxylic acid dianions have also been alkylated by reaction with aziridines to give novel y-amino substituted acids in good yields508. Methoxybenzoic acids have also been alkylated in a reductive process by reaction with lithium in ammonia followed by treatment with an alkyl halide. The product formed in this one-pot reaction is an alkylated cyclohexa-2,5-diene carboxylic acid507. 

A similar procedure with Bu SiCFj gave 4-(tributyisiloxy)-4-(trifluoromethyl)cyclohexa-2,5-dien-l-one yield 59%. 

A solution of 4-(tributylsiloxy)-4-(trifluoromcthyi)cyclohexa-2,5-dien-1-one (3.9 g. 10 mmol) in abs EtOH (10 mL) was treated successively with Zn dust (1.3 g. 20 mmol) and HOAc/H.O (4 1,10 mL). The mixture was heated to reflux for 1 h, allowed to cool to rt. and poured into HjO (100 mL). The resulting aqueous mixture was extracted with EtjO (3x.50mL). Combination, drying (MgSO ) and concentration of the FtjO layers afforded a residue, which was purified by short-path distillation to give the phenolic product yield 0.8 g (47%) bp 60 65 C/5 Torr. 

TCNQ Tetracyanoquinodimethane Systematic name Cyclohexa-2,5-diene-l,4-diylidene-bis(malononitrile)... 

Waring, A. J., Zaidi, J. H., Pilkington, J. W. Dienone-phenol rearrangements of bicyclic cyclohexa-2,5-dien-1-ones kinetic studies of the importance of a multistage mechanism. J. Chem. Soc., Perkin Trans. 21981, 935-939. 

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